1. Field of the Present Invention
The present invention relates to an electromagnetic induction system of induction loop, and more particularly, to an electromagnetic induction system with single-induction-loops and multi-induction-loop.
2. Description of the Prior Art
Since a handwriting input device can replace a mouse and allow users to input words and pictures by hand, more easily than a mouse, the field of improvement of a handwriting input device has developed rapidly in recent years. The early handwriting input device replaces a mouse with a pen. In order to increase the convenience of operation for the user, a cordless pointer device, such as a pen, a mouse or a stylus, and a digitizer tablet are usually used. The tip of the cordless pen or stylus corresponds with the left key of the mouse. Although conventional pen-input products have existed for several years, similar kinds of products generally focus on the application of a single function such as graphing, drawing or Chinese text key-in.
The conventional electromagnetic induction system is equipped with a digitizer tablet and a mouse or pen-transducer/pointer device. Generally speaking, there are two modes for presenting the position the pointer device located on the active area of the tablet: the relative mode and the absolute mode. The conventional mouse device generally functions in the relative mode, that is to say, when the mouse glides on the active area of digitizer tablet, the computer system receives an input from the mouse and it can only identify the relative movement in X and Y directions. A common technique is to implement a pair of mutually perpendicular altering signals in the mouse with an induction device, the pair of signals corresponding to the longitudinal and transverse movement of the mouse. In contrast, the cursor device of the tablet, such as cordless pointer device, generally functions in the absolute mode. As far as the computer system is concerned, once the pointer device is operated and moved to another place on the active area of the tablet, the signal changes in order to respond to a new absolute coordinates of the pointer device. Nowadays, there have already been several methods for positioning the pointer device on the active area of the tablet, and the electromagnetic field induction technique is the technique that generally applies to the absolute mode. The early transducer/pointer devices were connected to the tablet with multi-conductor wires, delivering the information of coordinates and switch/pressure status to the computer system with interface. Some cordless transducers/pointer devices in the prior art indicated the use of different functions by changing the frequency and/or phase, the functions included, pressing down the button, pressing the tip of the pointer device on the active area, and other similar functions. However, without careful handling, the change in frequency could easily cause misjudgment in the desired function of the pointer device because of various external factors such as metallic objects, noise signals, exterior electromagnetic fields, etc. These problems become extraordinarily obvious when it comes to tablets of larger size. The conventional technique for improvement made to the tablet system allows users to operate the pointer device with tablet system in dual mode, and therefore the information regarding relative mode and absolute mode can both be provided under the user's control.
The current pointer/input product is usually an electromagnetic induction system. The electromagnetic induction system usually comprises an electromagnetic pointer device and a digitizer tablet. The electromagnetic pointer device has a battery that provides energy for transmitting the relative electromagnetic signal and an oscillation circuit. Take the electromagnetic pointer device for example, when the tip of the pointer device is pressed, the inductance of the inductor changes, therefore the oscillation frequency also changes. The higher the pressure received by the pointer device is, the greater the inductance changes, and thus the greater the oscillation frequency changes. Therefore the amount of the pressure exerted upon the tip of the pointer device can be obtained through the changing degree of frequency. There are also two switch keys on the side of the cordless pointer device; the on/off status of switch keys changes connecting/disconnecting status of a specific capacitor in the oscillation circuits, and thus changes the transmitting frequency. When the user presses a switch key, it can be identified through detecting the variation of frequency. The tablet also comprises elements such as a detective loop, an amplifier, and an ADC and so on. The central writing area of this conventional handwriting tablet is plaited by induction loops, the layout being composed of double layers of a PCB and the induction loops with two axial arranged in an array of equal distance. The major use of these induction loops is to induce the electromagnetic signal transmitted by the electromagnetic pointer device. When the electromagnetic pointer device transmits the electromagnetic signal, these induction loops will induce the electromagnetic signal and the microprocessor will receive the processed information of the pointer device through a signal processing circuit.
Generally speaking, the induction loops of the conventional electromagnetic induction device and its layout design makes the induction loops a grid net with the X and Y axis arranged in an array at equal distance in order to induce the signal emitted from the electromagnetic pointer device and figure out its absolute coordinates. Referring to the induction loops layout deployed according to the X direction of a two-dimensional orthogonal coordinates indicated in FIG. 1A. One terminal of each direction loop 110A is connected respectively with one switch (from X1 to X25). The other terminal is connected with the common ground node 115, through which, the signal induced by each direction loop 110A can be obtained by controlling the switches X1 to X25 in order. Since the intensity of the magnetic field is an inverse proportion to the square of distance, the farther the distance between the electromagnetic pointer device that's transmitting the electromagnetic field and the induction loops, the weaker is the signal induced by the induction loops; in contrast, the nearer the distance between the electromagnetic pointer device that's transmitting the electromagnetic field and the induction loops, the stronger is the signal induced by the induction loops. Therefore, as long as the microprocessor of the tablet can scan through all the induction loops one by one in sequence, and analyze the strength of the signals induced by each induction loop, the induction loops in which dominates the range the electromagnetic pointer device located can be identified. The coordinates of its position can be figured out. However, as far as a tablet of a larger size is concerned, the number of induction loops arranged also increases, and therefore more loop switches are needed. In order to eliminate the defect of too many switches, the inventor of the present invention provides a method of increasing -type sections of induction loop for reducing the number of switches. As is shown in FIG. 1B, each induction loop (X1-X9 and XA-XC) is deployed in the direction of X axis of right-angled coordinates and is respectively composed by a plurality of -type sections 120. As far as each induction loop (X1-X9 and XA-XC) deployed in the same direction is concerned, each -type section 120 and other adjacent -type sections of it belong to different induction loops; therefore, the -type section on which locates the electromagnetic pointer device can be identified. For example, a -type section 120A of induction loop X5 and other adjacent -type sections 130 and 140 of induction loops of it belong respectively to induction loops X4 and X6. Besides, another -type section 120B of induction loop X5 and other adjacent -type sections 150 and 160 of induction loops of it belong respectively to induction loops X2 and XC. When the electromagnetic pointer device is located on -type section 120A or 120B of induction loop X5, whether the -type section on which locates the electromagnetic pointer device is 120A or 120B can be identified by referring signals produced by its adjacent induction loops X4, X6, XC, and X2. Therefore, according to what is said above, the number of switch in FIG. 1A (totaling 25 switches) is higher than that in FIG. 1B (totaling 12 switches). Besides, in conventional induction loop deployment, the distance between two adjacent -type sections of a same induction loop has to be noticed. Take distance “L” between two adjacent -type sections 120A and 120B of induction loop X5 for example, if the distance L is too short, misjudgment can be caused easily while identifying the location of electromagnetic pointer device.
On the other hand, the development of current information products is aimed at a high-speed and high data rate process with multiple and excellent functions. But as the speed of processing and data rate increase, the phenomenon of electromagnetic interference will happen often. Especially when the electromagnetic induction system is combined with other electronic devices in one system, the marginal part of induction loops will be interfered very easily by inductive electromagnetic fields. For example, when the induction loop is put on a Liquid Crystal Device Monitor Panel (LCD Monitor Panel), the marginal induction loop of electromagnetic induction system will be affected by electromagnetic interference made by Thin-Film Transistor (TFT) Driving IC on Liquid Crystal Device Monitor Panel and Power Inverter that lights up tube of LCD. Therefore, when LCD Monitor Panel is in operation, a variance electromagnetic field will form on the panel, which causes unbalanced deployment of induction loop magnetic field on the margin of electromagnetic induction system. As a result, when the induction loop receives signal, the electromagnetic field interferes the induction of induction loop, and thus causes poor linearity of marginal induction loop.
The above-mentioned problems are actually unavoidable as far as systems using induction loops are concerned. Especially when it comes to the tablet of a larger active area demanded in commerce, the number of its induction loops increases. Therefore, when the marginal induction loop is interfered by electromagnetic wave, the electromagnetic noise will also interfere other loop partitions following deployment of induction loop, which causes poor linearity of multi partitions and deteriorates quality of the electromagnetic induction system.